This paper investigates the optimization of the external polysilicon base sheet resistance of quasi self-aligned (QSA) SiGe:C HBTs from a 0.13 mu m BiCMOS process. Taking advantage of optimized implant conditions to improve the doping of the external base poly, and using an optimized non-selective epitaxy process with improved growth rate ratio of 1.7 between the polycrystalline silicon and monocrystalline silicon of the base, the maximum oscillation frequency f(max) reaches 300 GHz. (C) 2009 Elsevier B.V. All rights reserved.